The leaders of EU heavyweights Germany and France on Friday called for a new push to invigorate the bloc after Britain's shock Brexit vote.

Twenty-seven EU leaders will meet without Britain in Slovakia on September 16 and France's Francois Hollande and German Chancellor Angela Merkel said in a joint statement that a "new impulse" was required.

"With Brexit and the rise of populism and even questions on the very idea of Europe, a new impulse is needed for the European Union," they said.

"France and Germany will assume their responsibilities" to do this, they added.

British Prime Minister Theresa May has said she will not trigger Article 50-- the formal notification which starts a two-year negotiating period before Britain leaves the EU -- until next year at the earliest.

Speaking two days ahead of a G20 summit in Hangzhou in China, Hollande and Merkel underscored Europe's role in trying to spur growth and international trade.

"We will do our level best in China to see that the most important countries can give a new push to growth and global commerce," Hollande said.

Merkel on the other hand said that European countries "will do all they canto fight protectionism."